Anomalous Atomic Hydrogen Shock Pattern in a Supersonic Plasma Jet

Mazouffre, S.; Boogaarts, Mgh Maarten; Mullen, van der Jjam Joost; Schram, DC Daan

doi:10.1103/physrevlett.84.2622

Cited by 43 publications

(42 citation statements)

References 19 publications

(11 reference statements)

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“…The time-resolved study on collisional quenching of the two-photon LIF signal from low-temperature plasmas is reported in a separate paper, 34 as is the in-depth physical discussion of the expansion properties of the plasma jet. 32,35 …”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, only a few studies exist in which the LIF technique is applied to measure velocities of particles in plasmas, 30,31 and to the best of our knowledge our group was the first to report velocity measurements of ground-state atoms using the two-photon LIF technique. 32 In this study, two-photon excitation laser-induced fluorescence is applied to perform quantitative and spatially resolved measurements of the density, temperature, and velocity of ground-state hydrogen atoms in an expanding thermal Ar-H plasma created by a cascaded arc. The excitation and detection scheme for ground-state H applied in this work is the scheme that was originally demonstrated by Bokor et al in 1981.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

Boogaarts

Mazouffre

Brinkman

et al. 2002

Review of Scientific Instruments

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We report on quantitative, spatially resolved density, temperature, and velocity measurements on ground-state atomic hydrogen in an expanding thermal Ar-H plasma using two-photon excitation laser-induced fluorescence ͑LIF͒. The method's diagnostic value for application in this plasma is assessed by identifying and evaluating the possibly disturbing factors on the interpretation of the LIF signal in terms of density, temperature, and velocity. In order to obtain quantitative density numbers, the LIF setup is calibrated for H measurements using two different methods. A commonly applied calibration method, in which the LIF signal from a, by titration, known amount of H generated by a flow-tube reactor is used as a reference, is compared to a rather new calibration method, in which the H density in the plasma jet is derived from a measurement of the two-photon LIF signal generated from krypton at a well-known pressure, using a known Kr to H detection sensitivity ratio. The two methods yield nearly the same result, which validates the new H density calibration. Gauging the new ''rare gas method'' by the ''flow-tube reactor method,'' we find a krypton to hydrogen two-photon excitation cross section ratio Kr ͑2͒ / H (2) of 0.56, close to the reported value of 0.62. Since the H density calibration via two-photon LIF of krypton is experimentally far more easy than the one using a flow-tube reactor, it is foreseen that the ''rare gas method'' will become the method of choice in two-photon LIF experiments. The current two-photon LIF detection limit for H in the Ar-H plasma jet is 10 15 m Ϫ3 . The accuracy of the density measurements depends on the accuracy of the calibration, which is currently limited to 33%. The reproducibility depends on the signal-to-noise ͑S/N͒ ratio in the LIF measurements and is orders of magnitude better. The accuracy in the temperature determination also depends on the S/N ratio of the LIF signal and on the ratio between the Doppler-width of the transition and the linewidth of the excitation laser. Due to the small H mass, the current linewidth of the UV laser radiation is never the accuracy limiting factor in the H temperature determination, even not at room temperature. Quantitative velocity numbers are obtained by measuring the Doppler shift in the H two-photon excitation spectrum. Both the radial and axial velocity components are obtained by applying a perpendicular and an antiparallel excitation configuration, respectively. The required laser frequency calibration is accomplished by simultaneously recording the I 2 absorption spectrum with the fundamental frequency component of the laser system. This method, which is well-established in spectroscopic applications, enables us to achieve a relative accuracy in the transition frequency measurement below 10 Ϫ6 , corresponding to an accuracy in the velocity of approximately 200 m/s. This accuracy is nearly laser linewidth limited.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

Boogaarts

Mazouffre

Brinkman

et al. 2002

Review of Scientific Instruments

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“…Due to the surface recombination, the H atom density in the background is lower than in the expansion-the remaining density results from the diffusion of H atoms out of the expanding flow into the background. This effect is extensively described by Mazouffre et al 39,38 The collisional mean free path is several millimeters in the subsonic part of the flow. In the shock region the mean free path is even larger, in the order of the size of the expansion structure.…”

Section: B Rarified Expansionmentioning

confidence: 98%

Relaxation behavior of rovibrationally excited H2 in a rarefied expansion

Vankan

Schram

Engeln

2004

The Journal of Chemical Physics

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The evolution of the rotational and vibrational distributions of molecular hydrogen in a hydrogen plasma expansion is measured using laser induced fluorescence in the vacuum-UV range. The evolution of the distributions along the expansion axis shows the relaxation of the molecular hydrogen from the high temperature in the upstream region to the low ambient temperature in the downstream region. During the relaxation, the vibrational distribution, which has been recorded up to vϭ6, is almost frozen in the expansion and resembles a Boltzmann distribution at T Ϸ2200 K. However, the rotational distributions, which have been recorded up to Jϭ17 in vϭ2 and up to Jϭ11 in vϭ3, cannot be described with a single Boltzmann distribution. In the course of the expansion, the lower rotational levels (JϽ5) adapt quickly to the ambient temperature (Ϸ500 K), while the distribution of the higher rotational levels (JϾ7) is measured to be frozen in the expansion at a temperature between 2000 and 2500 K. A model based on rotation-translation energy transfer is used to describe the evolution of the rotational distribution of vibrational level vϭ2 in the plasma expansion. The behavior of the low rotational levels (JϽ5) is described satisfactory. However, the densities of the higher rotational levels decay faster than predicted.

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“…This so-called mass-defocusing effect has been reported in Ar-H 2 and pure H 2 plasma expansion. 12,13 In view of this effect the production efficiency of 2% is remarkably high.…”

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confidence: 97%

Absolute density measurements of ammonia produced via plasma-activated catalysis

Vankan

Rutten

Mazouffre

et al. 2002

Applied Physics Letters

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The generation of ammonia from atomic hydrogen and nitrogen has been demonstrated by means of cavity enhanced absorption spectroscopy. The atomic species are produced in a thermal plasma source in which plasma is created from mixtures of hydrogen and nitrogen. It is shown that for large atomic flux conditions, 2% of the hydrogen and nitrogen can be converted to ammonia. The process in which the ammonia molecules are formed from atomic radicals at the fully covered surface is called plasma-activated catalysis.

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Anomalous Atomic Hydrogen Shock Pattern in a Supersonic Plasma Jet

Cited by 43 publications

References 19 publications

Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

Relaxation behavior of rovibrationally excited H2 in a rarefied expansion

Absolute density measurements of ammonia produced via plasma-activated catalysis

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